Plastic optical member and light-quantity-controlling member each having a light-diffusing layer on its surface

ABSTRACT

PCT No. PCT/JP91/01177 Sec. 371 Date Apr. 27, 1992 Sec. 102(e) Date Apr. 27, 1992 PCT Filed Sep. 3, 1991 PCT Pub. No. WO92/04400 PCT Pub. Date Mar. 19, 1992.There is provided a plastics optical member having on its surface a light-diffusing layer composed of a layer of micro-joints formed by immersing a plastics material successively in a good solvent and a poor solvent, and a plastics light-quantity-controlling member having on its surface a white pattern composed of the micro-joints. The superiority in light diffuse reflection, transmission and light-quantity-controlling property permit their incorporation into various optical systems such as screens for projection, various displays, light-source-directly-under-an-illumination-surface type light boxes, edge light type light boxes, etc.

TECHNICAL FIELD

The present invention is a technique utilizing light diffusion, andrelates to a plastic optical member having a specific micro-joints layeron its surface, and a light-quantity-controlling member having a whitepattern of the aforementioned micro-joints on its surface.

Here, the term "optical member" refers to an optical member used in anypart of various optical systems in which light is desired to besubjected to diffuse reflection or diffuse transmission. Specificexamples thereof are optical members used in planar light sources,projection screens, window materials for building, various displays,office automation appliances, and precision optical instruments. Theterm "light-quantity-controlling member" refers to a specific opticalmember used for controlling the quantity of light. Specific examplesthereof are optical members for homogenizing the lightness of theillumination surface in the so-called "thin light box" such as abacklight used in liquid crystal displays of personal computers, aschaukasten for medical treatment, an electrically illuminated display,etc., to render the brightness uniform. The optical member and thelight-quantity-controlling member commonly utilize the light-diffusingproperties imparted by the provision of the aforementioned specificmicro-joints layer on the whole or a part of their surfaces.

BACKGROUND ART

Using conventional such as surface chemical treatment, sandblastingmethod (see JP-B-49-8711), coating with a light-diffusing white coatingmaterial (see, for example, JP-B-34-9168), etc., it is difficult toobtain on the surface of a plastic material a thin light-diffusing layerwhich can be formed partly or in the shape of a pattern, permitsadjustment of light diffuse reflection properties and light diffusetransmission properties, and can be formed not only on planar surfacesbut also on any curved surfaces. The reason for the difficulty isexplained below for each method.

In the surface chemical treatment, a violent reaction is carried outusing a strong acid, a strong base, etc., so that the spectralabsorption characteristics of the surface of the resultinglight-diffusing layer are changed by the chemical reaction. In otherwords, coloring and the like are caused. Moreover, the chemicaltreatment merely forms depressions and protuberances in the surface andhence does not impart significant light diffuse reflection properties orlight diffuse transmission properties to the surface. Furthermore, whenthe treatment is carried out so as to form a pattern, it is difficult toprepare a resist which is resistant to the above-mentioned violentchemical reaction.

In the sandblasting method, sand grains are caused to collide with aplastic material at high speeds. For the collision of the grains, highenergy is required. In addition, the finer the sand grains, the greaterthe air resistance, so that the fineness of the plastic material surfaceachieved by the treatment has its own limit and it cannot be expected toimpart very high light diffuse reflection properties or light diffusetransmission properties to the surface of the plastic material.

When a light-diffusing white coating material is applied on a plasticmaterial, the spectral absorption characteristics of the coated materialtend to be imbalanced because the light-diffusing white coating materialis composed of a white pigment, a binder, various additives, etc. Thereason is that in the case of such a coating material, coatingproperties should be given priority. It is difficult to make the contentof the white pigment in the coating material much higher than that ofthe binder from the viewpoint of the film-forming properties of thecoating material. In addition, in this case, it is the boundary surfacebetween the binder and the white pigment that scatters light. A smalldifference between their refractive indexes results in a smalllight-scattering effect. Therefore, if a large light diffuse reflectioneffect is desired, it is necessary to thicken the coating of thelight-diffusing white coating material, so that a thin light diffusereflective layer cannot be realized. Moreover, the light-diffusing whitecoating material is difficult to be applied on a curved surface.

On the other hand, conventional thin light boxes requiring a uniformillumination surface includes the following two types of light boxes:the so-called edge light type (see, for example, JP-A-57-128383 andJP-A-2-126501) which comprises a light-source provided at a side end ofan illumination surface, and a light-quantity-controlling member with alight guide panel having a reflective pattern formed thereon, whichmember diffuses light from the light source uniformly on theillumination surface; and the so-called lighting curtain type (see, forexample, JP-B-59-8809) which comprises a flat housing with anillumination surface on its open side, a light source provided in theflat housing and a light-quantity-controlling member provided rightabove the light source and containing a translucent reflector called"lighting curtain" which has a reflecting pattern, so as to allow lightfrom the light source to reflect repeatedly between the inner surface ofthe housing and the light-quantity controlling member to achieve uniformillumination.

The edge light type light box is disadvantageously heavy because it isused together with a light guide panel made of transparent plastic,glass or the like. The edge light type light box is disadvantageous inthat the area of light guide portion cannot be increased in proportionto the enlargement of the illumination surface since light is introducedthrough the end face of the light guide panel, so that the light box isdark.

The lighting curtain type light box is advantageous in that the lightbox is lightweight and very light because no light guide panel is usedtherein. However, its assembling is complicated because the positionalrelationship between the illumination surface and the reflective surfaceat the inner surface of the housing must be strictly set to obtain auniform illumination.

In both the edge light type light box and the lighting curtain typelight box, a regularly reflecting pattern such as a conventionalaluminum-deposited pattern as well as a printed pattern with a whitepigment is conventionally used as the reflecting pattern on thelight-quantity-controlling member. However, the regularly reflectingpattern has the shortcoming that parallax is caused on the illuminationsurface, depending on the angle from which the illumination surface islooked at, due to its directivity, although the regularly reflectingpattern has a high reflectance. The printed pattern with a white pigmentis disadvantageous in that the reflection wavelength characteristics ofthe pigment are shifted by various additives added to an ink forprinting in order to maintain the printability, resulting in theso-called color shift. Furthermore, in the case of a white patternobtained by printing, the size of dots constituting the pattern isrestricted by printing techniques and cannot be made very small.Therefore, the illumination surface requires an additional lightdiffuser panel for hiding a dot image since printing of dots with aninvisible size is difficult.

SUMMARY OF THE INVENTION

The present invention seeks to solve the various problems in theformation of a thin light-diffusing layer on the surface of a plastic aspresent material in the prior art, and provides a plastic optical membercomprising a plastic material as present having on the surface alight-diffusing layer which has adjustable diffuse reflection propertiesor light diffuse transmission properties, can be formed partly or in theshape of a pattern, on any curved surfaces, and has a flat spectralabsorption distribution. In addition, the present invention is seek tosolve the above-mentioned various problems in conventionallight-quantity-controlling means in light-quantity-controlling membersfor adjusting the quantity of transmitted light and the quantity ofreflected light, and provides a light-quantity-controlling member whichmakes it possible to obtain a bright box that is lightweight, verylight, and easy to construct and hardly causes parallax, and whichmember is free from color irregularities and has a simple structure.

Further in the present invention, these objects are achieved by forminga light-diffusing layer on the surface of a plastic material. Thelight-diffusing layer comprises micro-joints formed on the surface ofthe plastic material.

For forming such micro-joints, the plastic material is immersed in agood solvent (hereinafter referred to also as first solvent) for theconstituent plastic of the plastic material, and then in a poor solvent(hereinafter referred to also as second solvent) for the constituentplastic which is compatible with the first solvent. By this procedure,the light-diffusing layer is formed on the surface of the plasticmaterial. Each solvent may be either a single solvent or a mixedsolvent. In general, when an object is increased in volume by swelling,dissolution, melting, etc., and returns to its original state, itshrinks toward the centers of shrinkage scattered in the object. Owingto the cracks or spaces formed by the shrinkage between the centers ofshrinkage, numerous laminated structures in a pillar shape, a stringshape, a plate shape or a spherical shape are formed near the surface ofthe object, and they are called joints.

In some cases, the joint structures become spongy or felt-like dependingon the shrinkage rate and the flexibility and brittleness of the object.Their sizes reach several micrometers to several tens of centimeters insome cases.

The present inventors found that by the above-mentioned immersion of theplastic material in the good solvent and then in the poor solvent,extremely minute joints are formed on the surface of the plasticmaterial.

These micro-joints are assemblies of very small cracks formed byexpansion of a surface portion of the plastic material, followed by therapid shrinkage thereof. The cracks are formed in a very small size withvery high density in the surface portion of the plastic material.Furthermore, the cracks are formed in multi-layers in the direction ofthe depth of the plastic material. The cracks provide a very largeboundary surface area between air and the constituent plastic of theplastic material. Since light is scattered at the boundary surfaces,there are an extremely large number of portions from which light isscattered. Therefore, a large light-diffusing effect can be obtainedeven by using a thin light-diffusing layer.

When such a light-diffusing layer comprising micro-joints as describedabove is formed on the surface of a plastic material by treatment withthe solvents, the surface portion of the plastic material is at firstswollen by the immersion of the plastic material in a first solventwhich is a good solvent for the constituent plastic of the plasticmaterial. The swelling is caused by the expansion of the surface portionof the plastic material. This expansion is caused by the intrusion ofthe molecules of the solvent between the molecules of the constituentplastic. When the plastic material in this state is immersed in a secondsolvent which is a poor solvent for the plastic, the molecules of thefirst solvent present between the molecules of the plastic are replacedby the molecules of the second solvent, so that the molecules of theplastic are rapidly shrunk and solidified. Therefore, a large number ofcracks are formed and become micro-joints.

In this case, unless the first solvent and the second solvent arecompatible with each other, the molecules of the first solvent are notsmoothly replaced by the molecules of the second solvent, and hence nouniform micro-joints are formed. Therefore, the first solvent and thesecond solvent must be compatible with each other. Owing to thiscompatibility, the molecules of the first solvent are gradually replacedby the molecules of the second solvent as the ratio of the former to thelatter is changed, so that uniform micro-joints are formed.

Thus, the micro-joints according to the present invention have astructure composed of very small cracks and spaces integrated closelywith high density. The appearance of the micro-joints slightly variesdepending on the kind of the constituent plastic to be treated, thekinds of the first and second solvents, immersion method, immersiontemperature, immersion time, etc. For example, the micro-joints appearas assemblies of very small cracks or appear spongy or felt-like.However, the micro-joints serve as the light-diffusing layer of anoptical member, irrespective of their appearance.

The average thickness (depth) of the micro-joints layer obtained in thepresent invention is 1 to 30 μm. A micro-joints layer having an averagethickness of 10 to 20 μm is particularly preferable for alight-diffusing layer. The average distance between the cracks or spacesformed is 0.01 to 50 μm, and in particular, in an optical member ispreferably 0.02 to 20 μm.

The outstanding advantages of the micro-joints are as follows: themicro-joints provide a very high light diffuse reflectance (a highwhiteness degree of the surface); they do not peel off because they areintegral with the substrate (they have the same quality as that of thesubstrate) and provide a higher surface strength as compared with thecoating with a white pigment, etc. The micro-joints also have advantagesin their production. For example, their characteristics can easily bechosen by changing the kinds of the solvents employed and the conditionsof the treatment.

As regards the plastic material used as the optical member or thelight-quantity-controlling member of the present invention, themicro-joints layer can be formed on the surface of any kind of plasticso long as there is a good solvent for the plastic. Examples of plasticinclude homopolymers such as acrylic resin (e.g. PMMA), polyester resin(e.g. PET), polycarbonate, polyolefin (e.g. polyethylene), polystyrene,polyamide, polyoxymethylene, polyvinyl chloride and the like, andcopolymers such as ABS, AS and the like. These plastic can be used evenwhen they are not particularly transparent.

As a method for allowing the first solvent and the second solvent to acton the plastic, any methods can be employed, such as immersion in eachof the solvents, exposure to the vapor of each of the solvents, sprayingeach of the solvents onto the surface, coating of the surface with eachof the solvents, etc. Since the second solvent replaces the firstsolvent which has already swollen the surface portion of the plastic, itis necessary to supply a large amount of the second solvent to thesurface.

As described above, the plastic material having a light-diffusing layercomprising the micro-joints as a white surface for carrying out lightdiffuse reflection provides highly efficient and dense diffuse-reflectedlight. The plastic material can be employed for the production of adiffuse reflector used in various illuminators, a material constitutingthe inner surface of a light box, a projection screen, etc. Particularlywhen the material is utilized as a projection screen, a light and highlyclear projected image can be obtained owing to the thin light-diffusinglayer and the dense surface thereof.

The light-quantity-controlling member of the present invention foradjusting the quantity of transmitted light and for adjusting thequantity of reflected light has a light-quantity-controlling meanscomprising a white pattern comprising micro-joints formed on the surfaceof a plastic material. Such a light-quantity-controlling means can beformed as follows. Before forming the white pattern comprising themicro-joints, the surface of the plastic material is masked with aresist such as photoresist which is insoluble in both the first andsecond solvents, wherein the first solvent is a good solvent for theconstituent plastic, and the second solvent is a poor solvent for theconstituent plastic and is compatible with the first solvent. Theplastic material thus treated is immersed successively in the firstsolvent and then in the second solvent.

In the present invention, the surface of the plastic material in whichthe white pattern is to be formed is masked with a resist insoluble inboth the first solvent (a good solvent for the plastic material) and thesecond solvent (a poor solvent for the plastic material), while leavinga portion to be patterned. Then, the plastic material thus treated isimmersed in the first solvent. At this time, a portion not masked withthe resist is allowed to swell and increase in volume.

The immersion of the plastic material in the second solvent causes rapidreplacement of the first solvent by the second solvent due to thecompatibility between these solvents, and results in the rapid shrinkageand solidification of the swollen portion, which lead to the formationof numerous extremely minute cracks. Since the plastic material has lowcrystallinity, the cracks constitute a layer of the so-calledmicro-joints which are irregularly placed one upon another in a largenumber in the direction of the depth of the plastic material, as can beseen from FIG. 2 and FIG. 3 given hereinafter.

The removal of the solvent on the surface and of the resist forms asharp pattern composed of a micro-joints layer on the surface of theplastic material. The micro-joints in the white pattern constitute amultiple voids layer having an average distance between the voids of0.01 to 50 μm and an average layer thickness of 1 to 30 μm.

When the pattern comprising the micro-joints layer formed on the surfaceof the plastic material in the manner as described above is irradiatedwith light, the cast light carries out repeated reflection andrefraction due to the existence of a large number of the very smallcracks which are densely and irregularly overlaid in the direction ofthe depth of the plastic material. Therefore, in spite of the thinnessof the layer of the micro-joints, the pattern has a high whiteness and avery high non-directional reflectance.

As described above, the white pattern comprising a micro-joints layerrepeats reflection and refraction very many times in three dimensions inthe thin layer. Therefore, the white pattern exhibits extremelyexcellent effective diffusion, per unit transmittance, than does anetched surface or a sandblasted surface, whose diffusion is mainlyattributable to planar reflection and refraction. Accordingly, the whitepattern layer can be made thinner, whereby light loss is reduced.Therefore, the light-quantity-controlling member of the presentinvention having the white pattern comprising micro-joints efficientlyreflects or refracts the light thereby to enable accurate andnon-directional control of the light.

The light-quantity-controlling member of the present invention does notcontain any factor which changes the wavelength characteristics of thelight at the time when the member reflects or refracts the light.Therefore, the member does not cause color shift.

Embodiments of the present invention are explained below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one example of the surface of alight-diffusing layer comprising the micro-joints of the presentinvention observed under a microscope;

FIG. 2 is a schematic view of one example of a section of thelight-diffusing layer comprising the micro-joints;

FIG. 3 is a schematic illustration of the micro-joints of the presentinvention at a magnification of 5,000;

FIG. 4 is a partial perspective view of the light-quantity-controllingmember of the present invention;

FIG. 5 shows another example of the light-quantity-controlling member ofthe present invention. FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10 and FIG.11 are sectional side views of other examples of the present invention.

The symbols employed in these figures denote as follows.

1 - - - housing,

2 - - - light source,

3 - - - light-quantity-controlling member,

4 - - - light diffuser panel,

5 - - - reflective surface,

6 - - - white pattern,

7 - - - light-quantity-controlling member,

8 - - - white layer,

9 - - - transparent member,

10 - - - light-quantity-controlling member,

11 - - - light diffuse transmission member,

12 - - - reflective sheet,

13 - - - light guide member,

14 - - - reflecting pattern,

15 and 15' - - - white pattern comprising a micro-joints layer,

16 - - - light-quantity-controlling member,

17 - - - light-quantity-controlling member,

18 - - - housing.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is further illustrated below with examples.

EXAMPLE 1

A 30 mm×80 mm transparent polymethyl methacrylate plate was immersed indichloromethane (a first solvent) for 30 seconds and then in n-hexane (asecond solvent) for 60 seconds, and dried to form a whitelight-diffusing layer on the surface of the polymethyl methacrylateplate. In the formation of the light-diffusing layer, one side of thepolymethyl methacrylate plate was covered with an adhesive tape made ofpolyester so that the light-diffusing layer was formed only on the otherside of the polymethyl methacrylate plate which was exposed to thesolvents. After the formation of the light-diffusing layer, the adhesivetape was peeled off.

The reflection optical density of the light-diffusing layer thus formedon the surface of the polymethyl methacrylate plate was measured with aphotographic densitometer (Model P-2, mfd. by Fuji Photo Film Co., Ltd.)[the reflection optical density is expressed by the equation D=log (I₀/I) (log: common logarithm) wherein D is the value of the reflectionoptical density, I₀ is the intensity of an incident light, and I is theintensity of a reflected light]. A sheet of black felt was brought intoclose contact with the reverse side of a sample to be measured, wherebythe light transmitted through the light-diffusing layer was absorbed.

The reflection optical density of the light-diffusing layer formed onthe surface of the polymethyl methacrylate plate was 0.03, and the valuecorresponds to a reflectance of 93%. Thus, the light-diffusing layer hassufficient light diffuse reflection properties and hiding power as awhite layer.

Observation of the light-diffusing layer formed on the surface of thepolymethyl methacrylate plate under a microscope demonstrated that therewere micro-joints composed of numerous extremely minute and irregularcracks on the surface of the polymethyl methacrylate plate. As mentionedabove, the micro-joints observed under the microscope are schematicallyshown in FIG. 1.

Microscopic observation of a section of the polymethyl methacrylateplate having the light-diffusing layer on the surface revealed that thethickness of the light-diffusing layer was about 20 μm. The sectionobserved under a microscope is schematically shown in FIG. 2. Each ofFIG. 1 and FIG. 2 merely shows an example, and the size and shape of themicro-joints vary depending on the conditions at the formation of thelight-diffusing layer.

When visually observed, the light-diffusing layer formed on the surfaceof the polymethyl methacrylate plate was pure-white, had a very densesurface shape, and showed no directional property of surface profile atall. This is considered to be due to the non-crystalline, amorphousstructure of the polymethyl methacrylate plate.

For comparison, the same polymethyl methacrylate plate is sandblasted onone side and the above-mentioned reflection optical density wasmeasured. The reflection optical density was 0.62. When visuallyobserved, the sandblasted surface was not so white and was rough.

Next, a white coating material comprising titanium oxide as a whitepigment was applied on one side of a polymethyl methacrylate plate to athickness of 20 μm. The thickness was the same as that of the aforesaidlight-diffusing layer composed of the micro-joints formed by the methodof the present example. In this case, the reflection optical density was0.08. For further reducing the reflection optical density, the coatingthickness or the titanium oxide content in the white coating materialmay be increased. However, even when either of these factors isincreased, the application of the white coating material becomesdifficult and the formation of a dense layer on the surface of thepolymethyl methacrylate plate becomes impossible.

In the present example, the transparent polymethyl methacrylate platewas used merely for showing the result of evaluation of the formedlight-diffusing layer composed of the micro-joints in terms of thereflection optical density. As mentioned above, the plastic materialused in the present invention is not limited to transparent plasticplates.

In the method of the present example, it is sufficient to immerse theplastic material successively in the first solvent and then in thesecond solvent. Therefore, whatever shape the plastic material may have,the light-diffusing layer can be formed on the surface of the plasticmaterial in the same manner as described above.

EXAMPLE 2

A light diffuse reflective layer of micro-joints was formed on thesurface of each of 3 kinds of plastic plates in the same manner as inExample 1, except for replacing the first solvent and the secondsolvent. The reflection optical density was measured in the same manneras in Example 1.

For choosing solvents as the first solvent and the second solvent,respectively, the value of solubility parameter can be used.

The definition of solubility parameter is shown below: ##EQU1## SP:solubility parameter, ΔH: latent heat of vaporization,

R: gas constant (cal/mole),

C: density (g/cc),

M: gram-molecular weight (g/mol),

T: absolute temperature.

When a polymethyl methacrylate plate is used as a transparent plasticplate, the value of solubility parameter (hereinafter referred to as SPvalue) of the first solvent, i.e. the good solvent, is preferablybetween 9.0 and 9.8, more preferably between 9.3 and 9.7. It issufficient that the SP value of the second solvent, i.e. the poorsolvent, is 9.9 or more, or 8.8 or less. As the second solvent, therecan be exemplified alcohols, glycols, chain hydrocarbons and cyclichydrocarbons.

Table 1 shows examples of the formation of a light diffuse reflectivelayer of micro-joints in the surface of a polymethyl methacrylate plateby immersion of the polymethyl methacrylate plate in each of the firstsolvents having different solubility parameters for 30 seconds and thenin ethanol (SP value=12.7) as the second solvent for 60 seconds. For thelayers of micro-joints which remained transparent, the symbol T iswritten in the table instead of measuring the reflection opticaldensity.

                  TABLE 1                                                         ______________________________________                                                                 Reflection                                           First solvent   SP value optical density                                      ______________________________________                                        Xylene          8.8      T                                                    Benzene         9.2      0.83                                                 Chloroform      9.3      0.32                                                 Chlorobenzene   9.5      0.28                                                 Dichloromethane 9.7      0.34                                                 Dioxane         9.9      T                                                    ______________________________________                                    

Table 2 shows the results obtained under the same conditions as in Table1, except that n-hexane (SP value=7.3) was used as the second solvent.

                  TABLE 2                                                         ______________________________________                                                                 Reflection                                           First solvent   SP value optical density                                      ______________________________________                                        Xylene          8.8      T                                                    Benzene         9.2      1.24                                                 Chloroform      9.3      0.03                                                 Chlorobenzene   9.5      0.02                                                 Dichloromethane 9.7      0.03                                                 Dioxane         9.9      T                                                    ______________________________________                                    

Table 3 shows the results obtained under the same conditions as in Table1, except that dichloromethane (SP=9.7) was used as the first solventand each of various solvents was used as the second solvent.

                  TABLE 3                                                         ______________________________________                                                                 Reflection                                           Second solvent  SP value optical density                                      ______________________________________                                        Ethanol         12.7     0.34                                                 Dioxane         9.9      0.08                                                 Xylene          8.8      T                                                    Carbon tetrachloride                                                                          8.5      0.98                                                 Cyclohexanone   8.2      0.03                                                 n-Hexane        7.3      0.03                                                 ______________________________________                                    

When water was used as the second solvent, only large cracks were formedand no light diffuse reflective surface was formed.

From the above results, it was found that the first solvent can bechosen on the basis of SP value. The second solvents with relativelysmall SP value was able to form a micro-joints layer having higher lightdiffuse reflection property and more uniform structure than did thesecond solvents with relatively large SP values. This is because, at thetime of the immersion of the polymethyl methacrylate plate in the secondsolvent, the second solvents having a relatively large SP value replacedthe first solvent present on the surface of the plate more rapidly thandid the second solvents having a relatively small SP value. This is dueto the dominant influence of the solvent having a larger SP value in themixture of two solvents with different SP values.

Next, Table 4 shows examples of formation of a light diffuse reflectivelayer of micro-joints on the surface of a polycarbonate plate as atransparent plastic plate by immersion of the polycarbonate plate ineach of various first solvents for 30 seconds and then in n-hexane asthe second solvent for 60 seconds.

                  TABLE 4                                                         ______________________________________                                                                 Reflection                                           First solvent   SP value optical density                                      ______________________________________                                        Carbon tetrachloride                                                                          8.5      T                                                    Xylene          8.8      0.02                                                 Benzene         9.2      Nonuniform                                           Chloroform      9.3      Nonuniform                                           Dichloromethane 9.7      Nonuniform                                           Dioxane         9.9      0.24                                                 Acetone         10.0     T                                                    ______________________________________                                    

In the case where a light diffuse reflective layer of micro-joints isformed on the polycarbonate plate, a first solvent having an SP value offrom 8.6 to 9.9 is used for forming the light diffuse reflective layerof micro-joints. When a first solvent having an SP value of from 9.1 to9.7 is used, the surface portion of the polycarbonate plate is dissolvedin the first solvent and flows out when immersed in the second solvent.As a result, only a nonuniform light diffuse reflective layer ofmicro-joints is formed. Accordingly, it is necessary to select a solventhaving an appropriate solubility as the first solvent. As the secondsolvent used for the polycarbonate plate, a solvent having an SP valueof 8.5 or less or 10.5 or more can be used, and a solvent having an SPvalue of 8.0 or less is preferable. Use of a solvent having an SP valueof 8.0 to 8.5 as the second solvent reduces the light diffuse reflectionproperty of the formed layer. Use of a solvent having an SP value of10.5 or more as the second solvent makes the formation of a uniformlight diffuse reflective layer of micro-joints difficult.

Table 5 shows examples of formation of a light diffuse reflective layerof micro-joints on a polystyrene plate as a transparent plastic plate byimmersion of the polystyrene plate in each of various first solvents for30 seconds and then in n-hexane as second solvent for 60 seconds.

                  TABLE 5                                                         ______________________________________                                                                 Reflection                                           First solvent   Sp value optical density                                      ______________________________________                                        Methylcyclohexane                                                                             7.8      T                                                    Cyclohexane     8.2      0.08                                                 Carbon tetrachloride                                                                          8.6      0.04                                                 Benzene         9.2      Nonuniform                                           Dichloromethane 9.7      Nonuniform                                           Acetone         10.0     Nonuniform                                           Dibromomethane  10.4     T                                                    ______________________________________                                    

In the case where a light diffuse reflective layer of micro-joints isformed on the polystyrene plate, a first solvent having an SP value offrom 8.0 to 10.2 is used for forming the light diffuse reflective layerof micro-joints. When a first solvent having an SP value of from 8.5 to10.0 is used, the surface portion is dissolved in the first solvent andflows out when immersed in the second solvent. As a result, only anonuniform light-diffusing layer of micro-joints is formed. Accordingly,it is necessary to select a solvent having an appropriate solubility asthe first solvent. As the second solvent for the polystyrene plate, asolvent having an SP value of 8.0 or less or 10.5 or more can be used,and a solvent having an SP value of 8.0 or less is preferable forforming a uniform light-diffusing layer of micro-joints.

From the present example, it can be seen that light-diffusing layers ofmicro-joints in different states are formed by replacing the firstsolvent and the second solvent. This means that layers of micro-jointshaving various light diffuse reflection property can be formed byproperly choosing the first solvent and the second solvent. That is, themethod of the present example can be used not only for forming a lightdiffuse reflective white layer but also for forming a light diffusetransmission layer.

For all the samples produced in the present example, spectraltransmittance distribution was measured with a double beamspectrophotometer Model 124 manufactured by Hitachi, Ltd. which had beenequipped with an integrating sphere. As a result, it was found that thesamples showed the same characteristic distribution as that of theplastic plate serving as the substrate. Therefore, it can be seen thatthe formed light diffuse reflective layers of micro-joints are free fromshift of spectral absorption distribution, for example, coloring.

The present example indicates that a light diffuse reflective or lightdiffuse transmission layer of the micro-joints formed by the method ofthe present invention can be utilized not only for a light diffusereflector, as described in Example 1, but also for a light diffusetransmission panel. Therefore, the layer of micro-joints isadvantageously high in the density and efficiency in the utilization oflight when it is applied to a light diffuser panel used for providing aplanar light source using an electric lamp or a fluorescent lamp, atranslucent projection screen, a window material for a building, etc.

In the present example, a polymethyl methacrylate plate, a polycarbonateplate and a polystyrene plate were used as plastic plates. However, asdescribed above, any plastic can be used so long as it has a goodsolvent capable of swelling the surface of the plastic. Therefore, theplastic plate used for the present invention is not limited to the abovethree kinds of plastic plates.

Also, the transparency and shape of the above plastic plates are notlimiting factors of the present invention as neither are they in Example1.

In addition, the immersion times in the first solvent and the secondsolvent are determined as follows: When the immersion time in the firstsolvent is too long, the surface of the plastic plate is excessivelydissolved. When it is too short, no layer with sufficientlight-diffusing property can be obtained. Although no serious problem iscaused when the immersion time in the second solvent is too long, whenit is too short, no layer with sufficient light-diffusing property canbe obtained. The immersion times employed in the present example aremere examples and the optimum immersion time depends on specificconditions.

EXAMPLE 3

Example 2 reveals that the light diffuse reflection properties of alight diffuse reflective layer of the micro-joints formed on the surfaceof a transparent plastic plate vary depending on the kind of the firstsolvent and the second solvent selected on the basis of SP value.However, use of a single solvent does not permit optional, steplessadjustment of the light diffuse reflection property even when it isintended. Instead, a mixed solvent having an optionally synthesized SPvalue can be obtained by mixing two or more solvents having different SPvalues.

The examples below show the formation of a light diffuse reflectivelayer of micro-joints on the surface of a polmethyl methacrylate plateby immersing the plate successively in a first solvent obtained bymixing dichloromethane (SP value=9.7) and carbon tetrachloride (SPvalue=8.5), and n-hexane as the second solvent. In this case, adjustmentof the light diffuse reflection property of the layer of micro-jointswas proved to be possible by varying by steps the mixing ratio betweendichloromethane and carbon tetrachloride in the first solvent. Theimmersion times were 30 seconds in the first solvent and 60 seconds inthe second solvents. The results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Dichloromethane/carbon                                                        tetrachloride    Reflection optical density                                   ______________________________________                                        10/0             0.03                                                         9/1              0.03                                                         8/2              0.03                                                         7/3              0.03                                                         6/4              0.04                                                         5/5              0.07                                                         4/6              0.15                                                         3/7              0.53                                                         2/8              1.32                                                         1/9              T                                                             0/10            T                                                            ______________________________________                                    

Microscopic observation of a section of each of the samples showed thatin spite of the variation in thickness of light diffuse reflective layerof the micro-joint, the micro-joints themselves were similarly formed.

Although the mixing ratio was varied by steps of 10% in the above case,the light diffuse reflection property can be fairly finely adjusted byprecisely adjusting the mixing ratios within the range in which thelight diffuse reflection property is greatly influenced.

A layer of micro-joints having an optional light diffuse reflectionproperty can be formed by the use of a mixed solvent as in the presentexample, and it can be utilized in optical members for adjusting thequantity of light or light diffusion in precision optical instruments,etc. For example, uniform illumination can be achieved by properlyplacing the optical member possessing an adjusted light diffusereflection property in a light box used as a thin backlight used inoffice automatic appliances, etc. The optical member produced accordingto the method of the present example which has an optional surface lightdiffuse reflection property widens the degree of freedom of design ofsuch light boxes.

Although mixed solvents of dichloromethane and carbon tetrachloride wereused as examples of a mixed solvent in the present example, anycombination of solvents may be employed for forming on a plasticmaterial a layer of micro-joints possessing a desired light diffusereflection property.

Although a polymethyl methacrylate plate was used in the presentexample, any plastic may be used so long as they have a good solventcapable of swelling their surface.

In addition, a mixed solvent may be used as either the first solvent orthe second solvent. The same advantage as described above can beexpected by the use of a mixed solvent as the second solvent.

EXAMPLE 4

This example presents the production of a special screen for measurementused for projecting images on a hemispheric convex surface as an exampleof partially forming a light diffuse reflective layer of micro-joints ona plastic material.

An aqueous gelation solution was applied on the outside flat surface ofa hemisphere made of a polymethyl methacrylate, and dried. Thereafter,the whole body of the hemisphere was immersed in dichloromethane as afirst solvent for 30 seconds then in n-hexane as a second solvent for 60seconds. After drying, the hemisphere was immersed in boiling water toremove the gelatin applied on the flat surface of the hemisphere,whereby a polymethyl methacrylate hemisphere having a light diffusereflective layer of the micro-joints formed only on its curved surfaceportion was produced.

Thus, formation of a light diffuse reflective layer of micro-joints canbe prevented at a portion where the layer is not desired to be formed ona plastic material substrate by applying to the portion a solution of aresin (e.g. a water-soluble resin) which is not damaged by the first andsecond solvents and is soluble in another solvent not damaging theplastic material and drying the solution-applied substrate.

Since the method for forming a light diffuse reflective layer ofmicro-joints in the present invention comprises only successiveimmersion of a plastic material substrate in which the layer ofmicro-joints is to be formed in the first and second solvents, the layerof micro-joints can be formed irrespective of the shape of thesubstrate. In the case where the plastic material in which the layer ofmicro-joints is to be formed is large, the first and second solvents canbe allowed to act on the plastic material by using a shower or a sprayinstead of the immersion in the first and second solvents. Actually, anexperiment carried out by using a spray resulted in the same effect asthat obtained by the immersion.

Thus, a light diffuse reflective layer of micro-joints can be formed inparts on plastic materials of various shapes. Therefore, for example, anoptical member having both light diffuse reflection property and lightrefraction property can be produced by forming the layer of micro-jointson one side of a lens or one plane of a prism.

A specific example of the production is as follows. A reticle used inthe view finder of a single-lens reflex camera and a condenser lens tobe placed on the reticle could be integrally produced by forming thelayer of micro-joints only on the flat front surface of a lens with aflat front surface and convex rear surface. Thereby, a dense and brightview finder could be realized with reduction of the weight and number ofparts.

EXAMPLE 5

This example presents the production of an optical member for renderinglight uniform i.e. a light-quantity-controlling member, by adjusting thequantity of light by partial diffusion of light as an example offormation of a light diffuse reflective layer of micro-joints making apattern form on the surface of a plastic material.

A photosensitizer composed of an aqueous solution of a water-solubleresin and a photo-crosslinking agent was applied on one side of apolymethyl methacrylate plate and dried to form a photosensitive layer.Prior to the application of the photosensitizer, the whole surface ofthe opposite side of the polymethyl methacrylate plate had been coveredwith a polyester adhesive tape.

A film pattern mask or the like was placed on the photosensitive layers.The layer was exposed to ultraviolet light with a high pressure mercurylamp. The plate with the light-exposed layer was immersed in warm waterat 40° and the water was stirred. Thus, the unexposed portion of thephotosensitive surface was washed away. Thereafter, the polymethylmethacrylate plate was immersed successively in chloroform as a firstsolvent and n-hexane as a second solvent. In this step, a light diffusereflective layer of micro-joints was formed on the unexposed portion.Then, the polymethyl methacrylate plate was immersed in boiling water topeel off the crosslinked photosensitive layer. Finally, the polyesteradhesive tape on the opposite side was removed.

Thus, a pattern of a light diffuse reflective layer of micro-jointscould be formed on the surface of the polymethyl methacrylate plate.

In the present example, a water-soluble resin containing aphoto-crosslinking agent was selected as a resist layer for forming apattern of the light-diffusing layer of micro-joints. However, anyresists can be used so long as they are soluble in a solvent (adeveloping solvent) for washing away the portion not exposed to light,become insoluble by light irradiation, are peeled off from a plasticsubstrate by a peeling solvent to which the substrate is resistant, andare resistant to the first and second solvents.

For allowing the first and second solvents to act so as to form thepattern as described above, there can be employed not only immersion butalso showering and spraying.

A specific example of light-uniformizing techniques is the techniqueused in a backlight for displays for office automatic appliances, etc.Formation of a reflective-pattern on a transparent plate for renderinglight uniform by the method of the present example enabled theproduction of a thin backlight uniform in every angle.

Another method of rendering light uniform employed for a thin backlightis a technique called an edge light method. The technique comprisesallowing light from two fluorescent lamps to enter through the twofacing edges of a transparent plastic plate called a light guide panelso as to uniformly illuminate one flat side of the transparent plasticplate by diffused and reflected light by a pattern formed on theopposite flat side. Formation of a reflective pattern on a light guidepanel by the method of the present example enabled the preparation of auniform planar light source brighter than that prepared by a methodusing the prior art.

EXAMPLE 6

FIG. 5 is a sectional side view of a thin light box (alight-source-directly-under-an-illumination-surface type light box)using a light-quantity-controlling member, an example of the presentinvention. In the figure, a straight fluorescent tube 2 is provided as alight source in a flat box 1 having a reflective surface 5 formed on theinner wall, and a translucent diffuser panel 4 is provided as anillumination surface on the open side of the box 1. A light-controllingmember 3 called a lighting curtain is provided between the lightdiffuser panel 4 and the light source 2, whereby the brightness on theillumination surface is controlled so as to become uniform.

The lighting curtain 3 is produced by forming a pattern of dots of 25mesh composed of micro-joints on a polymethyl methacrylate plate(hereinafter referred to as acrylic plate) so that the density may bedecreased as the distance from the light source is increased.

Such a pattern of dots composed of a layer of micro-joints on thelighting curtain 3 was formed by covering one side of a transparentacrylic plate with a polyester adhesive tape; coating the opposite sidewith an aqueous solution containing 1 part of a condensation product ofp-diazophenylamine and paraformaldehyde and 19 parts of gelatin using a0.2 mm wire bar; drying the resulting coating while blowing air at roomtemperature to form a photoresist layer; bringing a silver salt filmhaving a pattern printed thereon into close contact with the photoresistlayer; exposing the film to light from a 1-KW high-pressure mercury lampfor 2 minutes; immersing the acrylic plate in warm water at 40° C. towash away the portion of the photoresist layer not exposed to the light;immersing the washed acrylic plate in chloroform as a first solvent for30 seconds; and then immersing the resulting plate in n-hexane as asecond solvent for 2 minutes to form a pattern of dots on the surface ofthe light-exposed surface of the acrylic plate. Finally, the photoresistlayer was peeled off using boiling water at 90° C.

The reflectance and transmission density of the lighting curtain 3 thusproduced were 95% and 1.80, respectively. The results show thesuperiority of the lighting curtain 3 in whiteness and light-diffusingproperty. The light box of FIG. 5 equipped with the lighting curtain 3was brighter than conventional light boxes by 10% or more. Nevertheless,it does not permit visual observation of the dots of the pattern norparallax. Accordingly, the construction of the light box was verysimple.

EXAMPLE 7

FIG. 6 is a sectional side view of a backlight equipped with alight-quantity-controlling member, another example of the presentinvention. This backlight was formed by attaching alight-quantity-controlling member 10 of the present invention to theopening of a flat box 1 having the same light source 2 as in Example 6in the interior.

The light-quantity-controlling member 10 was produced by forming apattern of white dots of 200 mesh composed of a layer of micro-joints onone side of a thin light diffuse transmissive member 11 (thickness: 1mm) made of an acrylic resin (a milk white plate #435, mfd. byMitsubishi Rayon Co., Ltd.) in the same manner as in Example 1.

The superiority in whiteness and diffuse reflection property of thelayer of micro-joints thus formed prevents projection of shadows by thedots on an illumination surface as caused by the dots formed bymetallizing in spite of the thinness of the light diffuse transmissivemember 11 made of plastic used as a substrate.

Therefore, the backlight of FIG. 6 equipped with thelight-quantity-controlling member 10 provided a very bright illuminationsurface. The illumination surface was free from parallax attributable tohigh light-diffusing property of the dots pattern. Also, it was freefrom light nonuniformity which tends to be caused by a slight change ofthe relation between the positions of the members. Accordingly, theconstruction of the backlight was very simple.

The substrate constituting the light-quantity-controlling member neednot be transparent as in the present example. Still higher performancecharacteristics of the light-quantity-controlling member can be achievedby using a plastic plate having, for example, a function of diffusinglight. Therefore, the plastic material used in the present inventionneed not be transparent.

EXAMPLE 8

FIG. 7 is a sectional side view of a backlight equipped with alight-quantity-controlling member of still another example of thepresent invention.

The figure shows a light box which comprises a flat box 1 having thesame reflective surface at the inner wall as in Example 6, a lightsource 2 provided in the flat box and a light-quantity-controllingmember 7 of the present invention attached to the opening of the box 1.

The light-quantity-controlling member 7 comprises a transparentpolycarbonate plate 9 having a thickness of 0.5 mm, a white layercomposed of a layer of micro-joints 8 formed on the whole surface of oneside of the plate and the same white layer of micro-joints 6 as abovehaving a pattern of dots of 200 mesh formed on the opposite side of theplate.

The dot density of the pattern of dots 6 on thelight-quantity-controlling member 7 is designed to be decreased as thedistance from the light source is increased. Repeated reflection of thelight from the light source 2 between the white pattern of dots 6 andthe reflective surface 5 on the inner wall of the box and diffusion ofthe light during its transmission through the white layer 8 on thesurface of the light-quantity-controlling member 7 results in uniformillumination on the surface of the light-quantity-controlling member 7.

The pattern of dots 6 was formed by masking one side of the transparentpolycarbonate plate 9 with the same photoresist as used in Example 1while leaving portions for pattern, and immersing the thus treated plate9 successively in xylene as a first solvent for 1 minute and n-hexane asa second solvent for 2 minutes.

The white layer 8 on the opposite side of the plate was formed bymasking the polycarbonate plate with gelatin while leaving the side tobe treated, and immersing the thus treated plate successively in a mixedsolvent of equal volumes of xylene and carbon tetrachloride as a firstsolvent and n-hexane as a second solvent for 30 seconds and 2 minutes,respectively.

The reflectance and transmission optical density of the thus formedpattern of micro-joints 6 on the light-quantity-controlling member 7were 96% and 1.83, respectively. The white layer on the front side had areflectance of 42% and a transmission optical density of 0.33. Thus,both the layers of micro-joints had very high light diffusing property.

The thin light box using the light-quantity-controlling member 7 thusproduced was free from parallax, permitted easy construction and showedno color shading at all, as did the light box in Example 6. Theunification of a lighting curtain and a light-diffusing member in onebody facilitated the construction of the light box than before.Moreover, the brightness of the light box could be improved by 20% ascompared with that produced by using a lighting curtain having aconventional pattern composed of an aluminum deposit and an acrylicresin diffuser panel. Furthermore, the weight of the light box could befairly reduced by making the light-quantity-controlling member 7 as athin plastic plate. Thus, a light box thinner than before was produced.It was most suitable as a backlight, for example, for a liquid crystaltelevision.

As shown in the present example, a polycarbonate plate can also be usedas a transparent plastic plate used for preparing thelight-quantity-controlling member as well as the acrylic plate. Variousplastic plates can be used in the same manner as above. The presentinvention is not limited to the above two kinds of plastic plates.

In the present example, the light-diffusing surface composed ofmicro-joins is not limited to a white surface having a high reflectance.A light-diffusing surface having a low reflectance, such as alight-translucent and diffusing surface, can also be formed instead ofthe white surface after forming the diffusing surface 8. That is, properselection of the first solvent or the second solvent enables impartingan optional reflectance to the light-diffusing surface within the rangeof from high reflectances to low reflectances. Imparting the optionalreflectance is possible in the case where a light-diffusing surface isformed on the whole surface as well as in the case where alight-diffusing surface is formed so as to make a pattern. In bothcases, the layer of micro-joints exhibits excellent diffusing property.

EXAMPLE 9

This example presents an example of the production of an edge light typelight guide panel by the process of the present invention.

FIG. 8 shows the structure of a conventional thin light box of edgelight type. FIG. 9 shows the structure of a thin light box of thepresent example. The conventional thin light box comprises a reflectivesheet 12, light sources 2 and 2, a light guide panel 13 and a diffusersheet 4. The thin light box of the present example has no componentcorresponding to the diffuser sheet 4. Therefore, in the conventionalthin light box, the front surface of the diffuser sheet 4 functions asan illumination surface. In contrast, in the thin light box of thepresent example, the front surface of the light guide panel 13 functionsas an illumination surface. In the conventional, edge light type, thinlight box, the main purpose of the provision of the diffuser sheet 4shown in FIG. 8 is to make invisible the reflective pattern formed onthe bottom surface of the light guide panel 13 which controls thequantity of light. Therefore, when this pattern of dots is so minutethat it cannot be perceived by eye, the diffuser sheet 4 becomesunnecessary. As a result, the efficiency of utilization of light isgreatly improved and the construction of the light box becomes easy bythe reduction of the number of parts.

The pattern of dots formed on the bottom surface of the light guidepanel for controlling the quantity of light may be a pattern of dots of200 mesh as in Example 2. However, by a conventional method comprisingscreen printing using ink containing a white pigment, such a minutepattern of dots cannot be formed. In addition, the efficiency ofutilization of light is low for the reflectance of a pattern of dotsformed by screen printing is about 80%.

A process for producing the light-quantity-controlling member alsoserving as a light guide panel in the present example is explainedbelow.

A photoresist layer having a pattern of dots of 200 mesh designed toprovide a uniform illuminance to an illumination surface was formed onone side of a transparent acrylic plate 13 (thickness: 2 mm) in the samemanner as in Example 6. The pattern was exposed to light and developed.Then, an aqueous gelatin solution was applied on the other side anddried. The plate 13 thus treated was immersed in chloroform as a firstsolvent for 30 seconds and then in n-hexane as a second solvent for 2minutes to form a pattern of micro-joints 15. Finally, the plate 13 wasimmersed in boiling water at 90° C. to peel off the gelatin layer on theopposite side of the side having a light-exposed photoresist portion.

Application of the light-quantity-controlling member 16 thus produced tothe thin light box of FIG. 9 improved the brightness of the illuminationsurface of the light box by 25% as compared with the thin light box ofFIG. 8 produced by the conventional method. This is due to the highreflectance of the pattern of dots (95%) as compared with theconventional ones (about 80%), improved light-diffusing property of thepattern, and the omission of the diffuser sheet 4. In the presentexample, the problem of parallax can be further reduced by dividing thediffuse reflective function of the pattern of micro-joints 15 into twoparts and imparting one part of the function to the top surface of thelight guide member 13 by the pattern 15 and another part to the bottomsurface of the light guide member 13 by the pattern 15'.

EXAMPLE 10

This example presents a method for obtaining a still brighter thin lightbox which comprises covering a fluorescent lamp 2 with a tubularlight-quantity-controlling member 17 as shown in FIG. 11. This method isfor uniformly illuminating the illumination surface on a diffusingmember 4 and comprises forming a pattern of dots for controlling thequantity of light on the outside surface of a pipe made of a polymethylmethacrylate (hereinafter referred to as acrylic pipe), inserting afluorescent lamp through the pipe and fixing the lamp in the pipe.

Although the use of the light-quantity-controlling member 17necessitates highly precise adjustment of the angle of placement of thelight-quantity-controlling member 17, it does not require so muchprecise adjustment of the other factors. Additionally, easy holding ofthe pipe-shaped, light-quantity-controlling member 17 in a light box ascompared with a plate-shaped one leads to easy construction of a lightbox and reduction of the weight of a light box. Moreover, placement ofthe light-quantity-controlling member 17 in the vicinity of a lightsource improves the efficiency of utilization of light.

When a metallized film is adopted to the light-quantity-controllingmember 17 in accordance with a conventional method, a very highprecision is required of its pattern of dots, because the metallizedfilm has no light-diffusing property. However, since thelight-quantity-controlling member is placed near the light source,luminance non-uniformity is induced on the illumination surface by theerrors caused by the thermal expansion of the substrate with theincrease of the temperature.

Another conventional method, in which a light-diffusing property isachieved, is a method comprising printing a pattern of dots with an inkcontaining a white pigment. However, highly precise printing of thepattern on a curved surface is extremely difficult by the method.Moreover, the method involves the following various problems caused bythe placement of the light-quantity-controlling member near the lightsource. For example, the light transmittance of the pattern of dots forcontrolling the quantity of light is too high; the pattern of dots isdiscolored with lapse of time due to its insufficient light resistance;and the pattern of dots is peeled off by the difference between thethermal expansion coefficients of a substrate and the pattern of dots.As discussed above, it was impossible to produce by the conventionalmethods such a light-quantity-controlling member that overcomes thedisadvantages.

In contrast, the pattern of micro-joints according to the presentinvention can be formed on a curved surface; it does not need to beformed with an extremely high precision since it is a diffusing pattern;it has a transmittance sufficiently low to control the quantity oflight; it is not peeled away from the substrate by the differencebetween the expansion coefficients of the substrate and the pattern andit has a light resistance equal to that of the resin of the substratebecause both the substrate and the pattern are made of the samematerial.

A process for producing the light-quantity-controlling member 17 of thepresent example is explained below.

The same water-soluble photoresist as used in Example 1 was applied onthe surface of an acrylic pipe. The pipe had an inside diameter a littlelarger than the external shape of a light source fluorescent lamp. Thephotoresist-applied acrylic pipe was then dried. Thereafter, around thedried acrylic pipe was wound a silver salt film on which the pattern ofdots designed to render uniform the luminance of an illumination surfacethat had been printed. The film-wound pipe was exposed to light from a1-kW mercury lamp (distance: 1 mm) for 5 minutes while rotating thepipe. The light-exposed pipe was immersed in warm water at 40° C. towash away the portion of the photoresist which had not been exposed tolight.

Then, both ends of the acrylic pipe were plugged with solvent-resistanceplugs such as Teflon™ plugs. Thereafter, the plugged pipe was immersedin chloroform as a first solvent for 30 seconds and then in n-hexane asa second solvent for 2 minutes to form a pattern of micro-joints.

Finally, the pattern-formed pipe was immersed in boiling water at 90° C.to peel off the portion of the photoresist which had been exposed tolight and the plugs at both ends were removed.

Applying the light-quantity-controlling member thus produced to a lightbox as shown in FIG. 10 could give a thin light box whose illuminationsurface was brighter than that of the light box obtained in example 6 by10% and exhibited more uniform luminance than that of the light boxobtained in example 6. The light-quantity-controlling member enabledeasy adjustment of the relation between the positions of the member anda light source and permitted relatively rough adjustment of the otherfactors, so that the construction of the thin light box was very simple.

As shown in the present example, the pattern of micro-joints can beformed not only on a flat surface but also on a curved surface, so thatit is possible to produce light-quantity-controlling members of variousshape as well as of plate shape.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, the variousproblems encountered in the formation of a very thin light diffusereflective layer on the surface of a plastic material by a conventionaltechnique have been solved. It is now possible to obtain a plasticoptical member comprising a plastic material having on the surface alight diffuse reflection layer with such advantages that the layer hadan adjustable light diffuse reflection property, it is formable in partsor so as to make a pattern, it is formable on any curved surfaces and itexhibits a flat spectral absorption distribution.

As a result, the application of the present invention to the lightdiffuse reflective surface, a section through which light is desired tobe diffuse reflected or diffuse transmitted, of an optical member (e.g.optical members used in planar light sources, projection screens, windowmaterials for building, various displays, office automatic appliances,and precision optical instruments) overcomes the various restrictionsand widens the applicability of the optical member to various parts thanbefore. Therefore, it is now possible to incorporate the optical memberhaving a highly precisely controlled, light diffuse reflective surfaceinto a precision optical systems. Moreover, according to the presentinvention, there can be provided such a light-quantity-controllingmember that solves various problems contained in the conventionallight-quantity-controlling means and that makes it possible to obtain alight box having a light weight, a bright illumination surface, easilyconstructible property, anti-parallax property, anti-color shadingproperty and simplicity in structure.

We claim:
 1. A plastic optical member comprising a plastic materialhaving a light-diffusing layer comprising micro-joints on at least apart of a surface of said plastic materialsaid micro-joints having astructure comprising very small cracks and spaces integrated closely athigh density at the surface of the plastic material, said cracks andspaces having an average spacing of 0.01 to 50 μm and thelight-diffusing layer of micro-joints having an average thickness of 1to 30 μm, and providing a very high light diffuse reflectance.
 2. Ascreen for projection which comprises a plastic optical member accordingto claim
 1. 3. A display which comprises a plastic optical memberaccording to claim
 1. 4. A plastic optical member according to claim 1,wherein said cracks and spaces of said micro-joints are constituted asirregular shrinkage centers formed in the surface of said plasticmaterial.
 5. A plastic light-quantity-controlling member having apattern of dots, said dots each comprising a multiplicity ofmicro-joints on a surface of the plastic member, said pattern of dotsbeing arranged to adjust the quantity of diffused, transmitted andreflected light by said member,said micro-joints constituting a layer ofmultiple voids having an average distance between said multiple voids of0.01 to 50 μm and an average thickness of said layer of 1 to 30 μm forproviding a high whiteness and a very high diffusion of reflected lightby repeated reflection and refraction of the light at said voids.
 6. Alight-source-directly-under-an-illumination surface type light box whichcomprises:a flat housing having an open side and an inner surface whichhas reflecting properties, a light source in said flat housing, and aplastic light-quantity-controlling member according to claim 5 provideddirectly above the light source.
 7. An edge light type light box whichcomprises:a light-quantity-controlling member according to claim 5 alsohaving a function of guiding light, said member comprising a plate witha flat front surface, a light diffuse-reflecting rear surface havingsaid pattern of dots comprising micro-joints and a set of flat facingends, a linear light source facing at least one of the ends of theplastic light-quantity-controlling member, and a light reflecting memberplaced at the diffuse-reflecting surface side of thelight-quantity-controlling member.
 8. A plasticlight-quantity-controlling member according to claim 5, in which saidmicro-joints are in the form of irregular shrinkage cracks provided insaid surface of said plastic member.